Gas driven pumps are used in a variety of applications. In some applications, the pumping capacity is less than the rate at which liquid flows into the pump environment; and in other applications the pumping capacity is greater than the rate of liquid inflow. In the former case, pumping rates are established in accordance with considerations other than the level of liquid in the pump environment. For example, in some applications an ejector pump is cycled through fill and discharge periods purely on the basis of time.
Where the pumping capacity exceeds the rate of liquid inflow, a number of mechanical and/or electrical devices e.g., floats, probes and switches have been employed to detect liquid levels to initiate and terminate pumping. Some mechanical and electrical devices are a liability in a liquid pumping environment; and they are particularly troublesome in an environment of dirty and/or chemically active or combustible liquids.